Methods and devices for communicating on a radio channel based on jointly encoding a preamble format with random access configuration

ABSTRACT

The invention relates to devices and methods for transmitting data on a radio channel comprising to jointly encode a preamble format with a first random access configuration, forming an extended random access configuration. The extended random access configuration is then transmitted on the radio channel.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/747,593, which was filed Jun. 11, 2010, which is a national stageapplication of PCT/SE2008/050934, filed Aug. 20, 2008, and claimsbenefit of U.S. Provisional Application 61/013,051, filed Dec. 12, 2007,the disclosures of each of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to methods and devices in atelecommunication system, in particular, for transmitting/receiving dataon a radio channel.

BACKGROUND

In modern cellular radio systems, a radio network has a strict controlon the behavior of a terminal. Uplink transmission parameters likefrequency, timing, and power are regulated via downlink controlsignaling from a base station to the terminal.

At power-on or after a long standby time, a user equipment (UE) is notsynchronized in the uplink. The UE can derive an uplink frequency andpower estimate from the downlink (control) signals. However, a timingestimate is difficult to make since the round-trip propagation delaybetween a base station, eNodeB, and the UE is unknown. So, even if UEuplink timing is synchronized to the downlink, it may arrive too late atthe eNodeB receiver because of propagation delays. Therefore, beforecommencing traffic, the UE has to carry out a Random Access (RA)procedure to the network. After the RA, the eNodeB can estimate thetiming misalignment of the UE uplink and send a correction message.During the RA, uplink parameters like timing and power are not veryaccurate. This poses extra challenges to the dimensioning of a RAprocedure.

Usually, a Physical Random Access Channel (PRACH) is provided for the UEto request access to the network. An access burst is used which containsa preamble with a specific sequence with good autocorrelationproperties. The PRACH may be orthogonal to the traffic channels. Forexample, in GSM a special PRACH time slot is defined. Because multipleUEs may request access at the same time, collisions may occur betweenthe requesting UEs. A contention resolution scheme has to be implementedto separate the UE transmissions. The RA scheme usually includes arandom back off mechanism. The timing uncertainty is accounted for byextra guard time in the PRACH slot. The power uncertainty is usuallyless of a problem as the PRACH is orthogonal to the traffic channels.

To distinguish between the different requesting UEs performing RAtypically many different RA preambles exist. A UE performing RA picksrandomly a preamble out of a pool and transmits it. The preamblerepresents a random UE ID which is used by a eNodeB when granting the UEaccess to the network via the eNodeB. The eNodeB receiver can resolve RAattempts performed with different preambles and send a response messageto each UE using the corresponding random UE IDs. In case thatrequesting UEs simultaneously use the same preamble a collision occursand most likely the RA attempts are not successful since the eNodeBcannot distinguish between the two users with a different random UE ID.

In E-UTRAN, evolved UMTS Terrestrial Radio Access Network, 64 preamblesare provided in each cell. Preambles assigned to adjacent cells aretypically different to insure that a RA in one cell does not trigger anyRA events in a neighboring cell. Information that must be broadcasted istherefore the set of preambles that can be used for RA in the currentcell.

Since E-UTRAN is capable of operation under very different operationconditions, from femto- and pico-cells up to macro-cells, differentrequirements are put on RA. Whereas the achievable signal quality for RAis less of a problem in small cells and more challenging in large cells.To also ensure that enough RA preamble energy is received, E-UTRANdefines different preamble formats. Only one such preamble format may beused in a cell and also this parameter must therefore be broadcasted.For Frequency Division Duplex, FDD, four preamble formats are defined.

Yet another parameter that is broadcasted is the exact time-frequencylocation of a RA resource, also called slot or opportunity. Such a RAtime resource spans always 1.08 MHz in frequency and either 1, 2, or 3ms in time, depending on the preamble format. For FDD, 16 configurationsexist, each defining a different RA time resource configuration.

In an FDD system in addition to the signaling required to point out the64 preambles that can be used in the current cell another 6 bits arerequired to indicate preamble format (2 bits) and RA subframeconfiguration (4 bits).

Referring to, for example, E-UTRAN time division duplex, TDD, mode, TDDmode has some particularities relative to the FDD mode which make asimple reuse impossible or impractical including, e.g., that TDD definesin total 5 RA preamble formats and not 4 requiring 3 bits to signal theformat. This additional preamble format will be called format 4 in thefollowing. The increased number of preamble formats thereby requires anincreased transmission capacity.

SUMMARY

It is an object of some embodiments to provide an efficient randomaccess configuration signaling between two communication devices.

Embodiments disclose a method in a second communication device fortransmitting data on a radio channel. The method comprises to jointlyencode a preamble format with a first random access configuration,forming an extended random access configuration, and transmitting theextended random access configuration on the radio channel.

The extended random access configuration makes the signalling moreefficient without the need of more transmission capacity.

Embodiments disclose a second communication device comprising a controlunit arranged to jointly encode a preamble format with a first randomaccess configuration. An extended random access configuration is therebyformed. The second communication device further comprises a transmittingarrangement adapted to transmit the extended random access configurationon a radio channel.

Embodiments disclose a method in a first device for performing a randomaccess process comprising to receive data containing an extended randomaccess configuration on a radio channel. The extended random accessconfiguration is decoded and thereby a preamble format and a firstrandom access configuration is retrieved. The preamble format and thefirst random access configuration is then used in order to perform arandom access process.

Embodiments disclose a first communication device comprising a receivingarrangement adapted to receive data on a radio channel from a secondcommunication device. The data comprises an extended random accessconfiguration. The first communication device further comprises acontrol unit being arranged to decode the extended random accessconfiguration to obtain a preamble format and a first radio accessconfiguration, and arranged to use the preamble format and the randomaccess configuration when performing a random access process.

By joint coding of RA configuration and preamble format only reasonablecombinations are encoded, resulting in, for example, that signalingoverhead is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described in more detail in relation to theenclosed drawings, in which:

FIG. 1 shows a schematic overview of a first communication devicecommunicating with a second communication device,

FIG. 2 shows a combined signaling and method diagram of a random accessprocedure,

FIG. 3 shows a table of extended random access configurations,

FIG. 4 shows a flow chart of a method in a second communication device,

FIG. 5 shows a schematic overview of a second communication device,

FIG. 6 shows a flow chart of a method in a first communication device,

FIG. 7 shows a schematic overview of a first communication device,

FIG. 8 shows a schematic overview of UL subframes within the duration ofone RA period,

FIG. 9 shows a schematic overview of examples how RA opportunities aremapped to uplink subframes, and

FIG. 10 shows a schematic overview of mapped resources when usingfrequency hopping.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present solution will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the solution are shown. This solution may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the solution to those skilled in the art. Likenumbers refer to like elements throughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”“comprising,” “includes” and/or “including” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

The present solution is described below with reference to block diagramsand/or flowchart illustrations of methods, apparatus (systems) and/orcomputer program products according to embodiments of the invention. Itis understood that several blocks of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor of a general purpose computer, special purpose computer,and/or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer and/or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the blockdiagrams and/or flowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the function/act specified in the block diagrams and/orflowchart block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

Accordingly, the present invention may be embodied in hardware and/or insoftware (including firmware, resident software, micro-code, etc.).Furthermore, the present invention may take the form of a computerprogram product on a computer-usable or computer-readable storage mediumhaving computer-usable or computer-readable program code embodied in themedium for use by or in connection with an instruction execution system.In the context of this document, a computer-usable or computer-readablemedium may be any medium that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device.

The computer-usable or computer-readable medium may be, for example butnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, device, or propagationmedium. More specific examples (a non-exhaustive list) of thecomputer-readable medium would include the following: an electricalconnection having one or more wires, a portable computer diskette, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,and a portable compact disc read-only memory (CD-ROM). Note that thecomputer-usable or computer-readable medium could even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory.

As used herein a communication device may be a wireless communicationsdevice. In the context of the invention, the wireless communicationdevice may e.g. be a node in a network such as a base station or thelike, a mobile phone, a PDA (Personal Digital Assistant) or any othertype of portable computer such as laptop computer.

The wireless network between the communication devices may be anynetwork such as an IEEE 802.11 type WLAN, a WiMAX, a HiperLAN, aBluetooth LAN, or a cellular mobile communications network such as aGPRS network, a third generation WCDMA network, or E-UTRAN. Given therapid development in communications, there will of course also be futuretype wireless communications networks with which the present inventionmay be embodied, but the actual design and function of the network isnot of primary concern for the solution.

In FIG. 1 a schematic overview of a first communication device 10communicating with a second communication device 20 is shown. Thecommunication is performed over a first interface 31 such as an airinterface or the like. In the illustrated example, the firstcommunication device 10 is a portable unit, such as a mobile phone, aPDA or the like and the second communication device 20 is a basestation, such as an eNobeB, NodeB, RBS or the like.

The second communication device sets up and transmits random access, RA,configurations in order for the first communication device to perform arandom access process. The RA related data comprising preamble format,RA configurations, such as, cyclic shift length, subframes to use forrandom access and the like.

The present invention proposes a joint encoding between preamble formatsand RA configurations. Since not all RA configurations are applicable toall RA preambles, for example, the RA preamble format requiring a RAresource duration of 3 ms cannot be scheduled every 2^(nd) subframe,i.e. every 2 ms, the joint encoding will improve the signaling.

By joint coding of RA configuration and preamble format the number ofreasonable combinations may be reduced enabling reuse of FDD signaling.

In the FDD mode of E-UTRAN, 6 different “densities” of RA opportunitiesare defined to accommodate the different expected loads on PRACH: 0.5,1, 2, 3, 5, and 10 RA opportunities within 10 ms independent of thesystem bandwidth. As a starting point it makes therefore sense to assumethese densities for TDD as well. In total there are 5 preamble formatsfor TDD and for each preamble format up to 6 densities resulting in 30different combinations. In addition it is desirable to have different“versions” of each combination. For example, in the case with 1 RAopportunity per 10 ms and preamble format 0 (basic preamble) it isdesirable to have 3 different patterns with the same density but wherethe RA opportunities are allocated at different sub-frames. This enablesan eNodeB that serves multiple cells to use different RA pattern acrossserved cells thus spreading processing load in time.

Thus, three versions multiplied with five preambles multiplied with sixdensities results in total in ninety combinations that need to beencoded. However, this exceeds the available number of six bits. Lookingmore detailed into the different combinations shows that not allcombinations actually make sense: Preamble formats 1 and 3 are designedfor very large cells where RA load is typically not so high. It isprobably for these formats not very important to support the highestdensities. Preamble format 3 furthermore requires three subframes whichmakes it for most common DL/UL splits impossible to support threedifferent versions not overlapping in time. The number of densities andversions could thus be reduced to 3×4=12 for format 1 and 2×2=4 forformat 3.

A reasonable set of supported densities for format 1 could be 0.5, 1, 2,and 3 RA opportunities within 10 ms. For format 3 only densities 0.5 and1 RA opportunities within 10 ms are supported. This results for format 0to 3 in total 3×6+3×4+3×6+2×2=52 combinations to encode.

With six bits, sixty four combinations may be encoded leaving twelvecombinations for format 4. This format 4 is special since it is veryshort and may only occur in a special field called Uplink PilotTimeslot, UpPTS. Because of its short duration the link budget of thispreamble is inferior compared to other preambles, therefore it isimportant to have different non-overlapping RA opportunities to create“interference-free” slots. It is important to support three differentversions leaving space for four densities for preamble format 4. Intotal 52+3×4=64 combinations exist. Table 1 summarizes these allocationsfor the different preambles. The proposed configurations are onlyexamples, it is of course possible to have more combinations for onepreamble format and less for another one or trade number of versions vs.number of densities.

TABLE 1 Example of version and density Preamble RA resources format per10 ms # Versions 0 0.5, 1, 2, 3, 5, 10 3 1 0.5, 1, 2, 3 3 2 0.5, 1, 2,3, 5, 10 3 3 0.5, 1 2 4 www, xxx, yyy, zzz 3

Another possibility is to generally support at the most five densitiesand not six when assuming that the 6^(th) density (10 RA opportunitiesin 10 ms) is very high. Using the same arguments as above, the densitiesand number of versions shown in table 2 are obtained for the differentpreamble formats. Here is one combination reserved for future use. Alsothis set of combinations is only an example and different tradeoffsbetween preamble formats and densities vs. versions can also be madehere.

TABLE 2 Another example of version and density allocation for differentpreamble formats Preamble RA resources format per 10 ms # Versions 00.5, 1, 2, 3, 5 3 1 0.5, 1, 2, 3 3 2 0.5, 1, 2, 3,5 3 3 0.5, 1 3 4 5different densities 3

In the following a combination of preamble format, density, and versionis referred to as extended RA configuration.

Even though above explanations were done in the context of a TDD systemthe same ideas are also applicable to a half-duplex FDD system.

In FIG. 2, an example of a schematic combined signaling and methoddiagram between a first communication device 10 and a secondcommunication device 20 is shown. The first communication device 10 maybe a user equipment UE, such as a mobile phone, a PDA, or the like. Thesecond communication device 20 may be a base station, such as a RBS,NodeB, eNodeB, a combined RBS and RNC, or the like.

In step S10, the second communication device 20 jointly encodes apreamble format with a first random access configuration, forming anextended random access configuration.

In step S20, the second communication device 20 transmits the extendedrandom access configuration on a radio channel, such as a broadcastchannel or the like.

In step S30, the first communication device 10 receives the extendedrandom access configuration on the broadcast channel and processes theextended random access configuration by, for example, looking up theextended random access configuration value in a stored table of extendedrandom access configurations. Thereby, the first communication device 10determines what preamble format and random access configuration to usewhen performing a random access process.

In step S40, the first communication device 10 transmits a random accessrequest to gain access to a network on, for example, a physical randomaccess channel PRACH using the preamble format and the random accessconfiguration to the second communication device 20.

In step S50, the second communication device 20 process the randomaccess request in order to allow or decline access to a network. Thesecond communication device 20 may as well confirm reception of therandom access request.

It should be noted that the UE may transmit the access request to adifferent communication device, base station; this might be the caseduring, for example, handover. In this case, wherein the firstcommunication device 10 performs a random access procedure with adifferent communication device, the different communication deviceprocesses the random access request.

In FIG. 3, a schematic overview of a table listing extended randomaccess configurations and the corresponding preamble format, PRACHdensity value and version index is provided.

In a first column C1 PRACH configuration index is indicated. Each PRACHconfiguration index, that is, the extended random access configuration,corresponds to a certain combination of a preamble format, a PRACHdensity value and a version index. The preamble format is listed in asecond column C2, density per 10 ms in a third column C3, and theversion in a fourth column C4.

In FIG. 4, a schematic flow chart of a method in a second communicationdevice is shown.

In optional step S2, the second communication device determines a firstrandom access configuration and a preamble format to use in a cell ofthe second communication device. The determination may be based on thesize of the cell and the like. These random access settings may also bemanually inputted during installation or setup.

In step S4, the second communication device jointly encodes thedetermined preamble format with the first random access configuration,forming an extended random access configuration. The extended randomaccess configuration may in some embodiments correspond to a combinationof a preamble format, a density value of a Physical Random AccessChannel and a version index defined in a table.

Within one radio frame we have multiple RA opportunities according tothe RA density. Each RA opportunity consists of a number of subframes,for example, 1, 2, or 3 subframes, depending on the preamble format.

A version may be defined by a collection of random access opportunitiesbelonging to the cell of the second communication device.

The extended random access configuration may in some embodiments requiremaximum six bits.

The preamble format may be one out of five preamble formats.

In step S6, the second communication device transmits the extendedrandom access configuration on a radio channel in the cell of the secondcommunication device.

The radio channel may in some embodiments be a broadcast channel.

In order to perform the method steps a second communication device isprovided. The second communication device 20 may be a base station, suchas a RBS, NodeB, eNodeB, a combined RBS and RNC, or the like.

In FIG. 5 a schematic overview of a second communication device 20 isshown.

The second communication device 20 comprises a control unit CPU 201,such as a μprocessor, a plurality of processors or the like, configuredto jointly encode a preamble format with a first random accessconfiguration, thereby forming an extended random access configuration.The first random access configuration may correspond to a combination ofa density value of a Physical Random Access Channel and a version index.The control unit 201 may further create a data packet comprising theextended random access configuration, for example, a value of six bits.

In addition, the control unit 201 may, in some embodiments, be arrangedto determine cell related parameters, such as, the first random accessconfigurations, the preamble format and/or the like. The determinationmay be performed in real time based on load, size of a cell and/or thelike. The values of preamble format, random access configurations andthe like may also be inputted manually.

The second communication device 20 further comprises a transmittingarrangement 205 adapted to transmit the data packet comprising theextended random access configuration. The data packet is transmittedover a radio channel of the cell of the second communication device 20.The radio channel may be, for example, a broadcast channel.

The second communication device 20 may further comprise a receivingarrangement 203 adapted to receive data from different communicationdevices, for example, a first communication device using the preambleformat and the first random access configuration on, for example, aphysical random access channel.

In the illustrated example, the second communication device 20 comprisesa memory unit 207 arranged to have application installed thereon thatwhen executed on the control unit makes the control unit perform themethod steps. Furthermore, the memory unit 207 may have data stored,such as random access related data or the like, thereon. The data maycomprise a table listing extended random access configurations and thecorresponding preamble format, PRACH density value and version indexthat may be used when creating the data packet. The memory unit 207 maybe a single unit or a number of memory units.

Furthermore, the second communication device 20 may comprise aninterface 209 for communicating with, for example, a network to which afirst communication device requests access.

In FIG. 6 a schematic flow chart of a method in a first communicationdevice is shown.

In step R4, the first communication device receives data containing anextended random access configuration over a radio channel. The radiochannel may be a broadcast channel or the like.

In step R6, the first communication device decodes the received data,reading the extended random access configuration as, for example, avalue of maximum six bits. The extended random access configurationvalue may from a table generate a preamble format and a random accessconfiguration. In some embodiments, the random access configurationcomprises a combination of a density of a PRACH and a version index. Asstated above, a version may be defined by a collection of random accessopportunities belonging to a cell of the second communication device.

In optional step R8, the first communication device performs a randomaccess process using the preamble format and the first random accessconfiguration.

The random access process may be performed to the second communicationdevice, base station, or a different communication device, such as adifferent base station. This may be the case when a handover isperformed.

In order to perform the random access procedure a first communicationdevice is provided. The first communication device may be a userequipment, such as, a mobile phone, a PDA or the like.

In FIG. 7, a schematic overview of a first communication device 10 isshown.

The first communication device 10 comprises a receiving arrangement 103adapted to receive data over a radio channel, such as a broadcastchannel or the like, from a second communication device. The datacomprises an extended random access configuration.

The first communication device 10 further comprises a control unit 101arranged to decode the extended random access configuration to obtain apreamble format and a first radio access configuration. The extendedrandom access configuration may be a value of maximum six bits and bycomparing the extended random access configuration value with indexvalues in a table a preamble format, a density value of a PRACH and aversion index may be retrieved, upon matching of values.

The control unit 101 may additionally be arranged to perform a randomaccess process in order to access a network. In the random accessprocess, the control unit 101 uses the preamble format and the randomaccess configuration and transmits the connection request using atransmitting arrangement 105.

The first communication device 10 may further contain a memoryarrangement 107, comprising a single memory unit or a number of memoryunits. Applications arranged to be executed on the control unit may bestored on the memory that when executed on the control unit makes thecontrol unit perform the method steps. Furthermore, the memory unit 207may have data stored thereon, such as RA configurations data, such as,preamble format, random access configurations and the like. The data maycomprise a table listing extended random access configurations and thecorresponding preamble format, PRACH density value and version indexthat may be used when creating the data packet. The memory unit 207 maybe a single unit or a number of memory units.

It should be noted that a version may be defined by a collection ofrandom access opportunities belonging to the cell of the secondcommunication device.

The extended random access configuration may in some embodiments requiremaximum six bits.

The preamble format may be one of five preamble formats.

It should be understood that the receiving and transmitting arrangementsin the communication devices may be separated devices or arranged as acombined device, such as a transceiving unit or the like.

Depending on the DL/UL allocation the different RA configurations havedifferent interpretations. In order to reduce the required signaling itis therefore proposed to number the subframes allocated to RA in termsof UL subframes rather than subframes.

One possibility may be to define for each extended RA configuration andeach possible DL/UL allocation a pattern describing the UL subframes andfrequency region allocated to RA. In addition to DL/UL split the systembandwidth also has an impact since for lower system bandwidth lessfrequency regions are available than for higher bandwidth.

A more systematic approach is described in the following: In FIG. 8 allUL subframes within the duration of one RA period are shown. RAsubframes are denoted 81 and non RA subframes are denoted as 83. The RAperiod is 10 ms for RA densities larger or equal to 1 per 10 ms and 20ms for 0.5 RA opportunities per 10 ms. The number of UL subframes withinthe RA period is denoted L. The number of subframes allocated to each RAresource is M. N is then the number of RA resources that can be placednon-overlapping in each RA period. The considered extended RAconfiguration has a density of D RA opportunities within the RA period.The gaps Δ1 and Δ2 are the numbers of UL subframes between twoconsecutive RA resources and the number of RA subframes left after thelast RA subframe, respectively. R denotes the number of differentversions that exist of the given extended RA configuration.

$N = {\min\left( {\left\lfloor \frac{L}{M} \right\rfloor,{R \cdot D}} \right)}$$\Delta_{1} = \left\lfloor \frac{L - {N \cdot M}}{N} \right\rfloor$Δ₂ = L − N ⋅ M − (N − 1) ⋅ Δ₁

The number t_(l,k) to be the UL subframe number where RA opportunity kof version l of the given extended RA configuration starts. Here isassumed that the numbering of UL subframes and versions start with 0. Ifnot enough versions may be placed non-overlapping into one RA period theplacement starts over starting from UL subframe 0 at another frequency.Further, the number f_(l,k) denotes the logical index to the predefinedfrequency at which RA opportunity k of version l is located at (logicalindex since the predefined frequencies neither have to be contiguous norassigned to monotonic increasing/decreasing frequencies). Since in totalonly N_(RA/BW) predefined RA frequency regions exist a modulo operationsis required to constrain the allocated frequency band to thosepredefined frequencies. For smaller system bandwidth not enough RAfrequency bands N_(RA/BW) may exist and placement of different RAresources overlap.

t_(k, l) = (k ⋅ D + l mod N) ⋅ (M + Δ₁)$f_{k,l} = {\left\lfloor \frac{{k \cdot D} + l}{N} \right\rfloor{mod}\; N_{{RA}/{BW}}}$

FIG. 9 shows different examples of extended RA configurations and theiractual mapping to UL subframes.

In the top figure the RA opportunity 0 of version 0 is firstly allocatedfollowed by opportunity 0 of versions 1 and 2, that is, l=1 and 2. RAopportunity 1 of version 0 is then allocated along the time domain andRA opportunity 1 of versions 1 and 2 are allocated in a differentfrequency.

In the middle figure, the RA opportunity 0, version 0 is followed by RAopportunity 0 of versions 1. RA opportunity 0 of version 2 is thenfrequency multiplexed into the same UL subframes as RA opportunity 0 ofversion 0. Here one RA opportunity consists of 2 UL subframes.

In the lower figure, each version is allocated at different frequencies.

The simplest way to define the predefined RA frequency regions is toextend the concept from FDD where these regions are placed at the bandedges of the uplink shared channel. If multiple RA resources aredistributed over time within a RA period (i.e. N>1) the position ofthese frequency regions may hop according to a predefined hoppingpattern. In the simplest case the only allowed hopping positions are atthe two band edges of the uplink shared channel.

FIG. 10 depicts examples how such a frequency hopping could look like.In FIG. 10, it is shown how logical index -LI-, also denoted as f_(l,k)in the formula above, is mapped to physical frequencies.

The described way is an example how to calculate the exact mapping of ULsubframes to RA subframes. Important is 1) to try to spread outopportunities in time and 2) (if not enough UL subframes are availableto separate all opportunities of a version in time) to place multiple RAsubframes into the same UL subframe(s) at different frequencies.

In the drawings and specification, there have been disclosed exemplaryembodiments of the invention. However, many variations and modificationscan be made to these embodiments without substantially departing fromthe principles of the present invention. Accordingly, although specificterms are employed, they are used in a generic and descriptive senseonly and not for purposes of limitation, the scope of the inventionbeing defined by the following claims.

The invention claimed is:
 1. A method in a base station of an evolvedUMTS Terrestrial Radio Access Network, E-UTRAN, operating in timedivisional duplex, TDD, mode for transmitting data on a radio channel,the method comprising: jointly encoding a preamble format with a firstrandom access configuration, forming an extended random accessconfiguration, wherein the first random access configuration comprises acombination of: a density value defining a density of random accessopportunities on a Physical Random Access Channel, PRACH; and a versionindex defining one of several possible patterns of opportunities on thePRACH for that density, each pattern allocating opportunities todifferent sub-frames of the PRACH; and transmitting the extended randomaccess configuration on the radio channel.
 2. The method of claim 1,further comprising determining the first random access configuration andthe preamble format to use in a cell of the base station.
 3. The methodof claim 2, wherein said determining comprises selecting the firstrandom access configuration and the preamble format from a subset ofnominally possible combinations of a first random access configurationand a preamble format, wherein the subset includes a number of possiblecombinations less than the number of nominally possible combinations. 4.The method of claim 3, wherein the subset excludes at least one of: anominally possible combination of a preamble format having a first valueand a first random access configuration that comprises a density valuehigher than a defined threshold; and a nominally possible combination ofa preamble format having a second value and a first random accessconfiguration that comprises a density value higher than the definedthreshold and a version index having a third value.
 5. The method ofclaim 1, wherein the extended random access configuration comprises amaximum of six bits.
 6. The method of claim 1, wherein the radio channelcomprises a broadcast channel.
 7. A base station of an evolved UMTSTerrestrial Radio Access Network, EUTRAN, configured to operate in timedivisional duplex, TDD, mode, the base station comprising: controlcircuit configured to jointly encode a preamble format with a firstrandom access configuration, thereby forming an extended random accessconfiguration, wherein the first random access configuration comprises acombination of: a density value defining a density of random accessopportunities on a Physical Random Access Channel, PRACH; and a versionindex defining one of several possible patterns of opportunities on thePRACH for that density, each pattern allocating opportunities todifferent sub-frames of the PRACH; and a transmitting circuit configuredto transmit the extended random access configuration on a radio channel.8. The base station of claim 7, wherein the control circuit is furtherconfigured to determine the first random access configuration and thepreamble format to use in a cell of the base station.
 9. The basestation of claim 8, wherein the control circuit is configured to selectthe first random access configuration and the preamble format from asubset of nominally possible combinations of a first random accessconfiguration and a preamble format, wherein the subset includes anumber of possible combinations less than the number of nominallypossible combinations.
 10. The base station of claim 9, wherein thesubset excludes at least one of: a nominally possible combination of apreamble format having a first value and a first random accessconfiguration that comprises a density value higher than a definedthreshold; and a nominally possible combination of a preamble formathaving a second value and a first random access configuration thatcomprises a density value higher than the defined threshold and aversion index having a third value.
 11. The base station of claim 7,further comprising a receiving circuit configured to receive randomaccess data from a user equipment, and wherein the control circuit isconfigured to process the random access data.
 12. The base station ofclaim 7, wherein the extended random access configuration comprises amaximum of six bits.
 13. The base station of claim 7, wherein the radiochannel comprises a broadcast channel.
 14. A method in a user equipmentof an evolved UMTS Terrestrial Radio Access Network, E-UTRAN, operatingin time divisional duplex, TDD, mode for performing a random accessprocess, the method comprising: receiving on a radio channel datacontaining an extended random access configuration, decoding theextended random access configuration, thereby retrieving a preambleformat and a first random access configuration. wherein the first randomaccess configuration comprises a combination of: a density valuedefining a density of random access opportunities on a Physical RandomAccess Channel, PRACH; and a version index defining one of severalpossible patterns of opportunities on the PRACH for that density, eachpattern allocating opportunities to different sub-frames of the PRACH;and performing a random access process using the preamble format and thefirst random access configuration.
 15. The method of claim 14, whereinthe extended random access configuration comprises a maximum of sixbits.
 16. The method of claim 14, wherein receiving said data comprisesreceiving said data on a broadcast channel.
 17. A User Equipment of anevolved UMTS Terrestrial Radio Access Network, E-UTRAN, configured tooperate in time divisional duplex, TDD, mode, the User Equipmentcomprising: a receiving circuit configured to receive on a radio channeldata comprising an extended random access configuration; a controlcircuit configured to decode the extended random access configuration toobtain a preamble format and a first random access configuration, thefirst random access configuration comprising a combination of: a densityvalue defining a density of random access opportunities on a PhysicalRandom Access Channel, PRACH; and a version index defining one ofseveral possible patterns of opportunities on the PRACH for thatdensity, each pattern allocating opportunities to different sub-framesof the PRACH; and wherein the control circuit is further configured toperform a random access process using the preamble format and the randomaccess configuration.
 18. The User Equipment of claim 17, wherein theextended random access configuration comprises a maximum of six bits.19. The User Equipment of claim 17, further comprising a transmittingcircuit configured to transmit a random access request using thepreamble format and the random access configuration.
 20. The UserEquipment of claim 17, wherein the receiving circuit is configured toreceive data on a radio channel that comprises a broadcast channel.